1. Field of the Invention
The present invention is concerned with liquid crystalline acetylene derivative, liquid crystalline mixtures which contain these compounds and their use for electro-optical purposes.
2. Background
Since the optical properties of liquid crystals can be influenced by an applied voltage, such substances are primarily used as dielectrics in indicating devices. Electro-optical devices based on liquid crystals are well-known to a person skilled in the art and can be based on various effects. The most common indicating devices are based on the Schadt-Helfrich effect and have a twisted nematic structure. Examples of such cells are TN cells ("twisted nematic") and STN cells (super-twisted nematic).
The liquid crystal materials for such cells must have a good chemical and thermal stability and a good stability towards electric fields and electromagnetic radiation. Further, the liquid crystal materials should have a low viscosity and in the cells should give short response times, low threshold potentials and a high contrast. At the usual operating temperatures they should have a suitable mesophase; for example, a nematic or cholesteric mesophase for the aforementioned cells. Further, the dielectric anisotropy should be as high as possible.
Since liquid crystals are usually used as mixtures of several components, it is also important that the components have a good miscibility with one another.
Liquid crystalline compounds which satisfy the aforementioned requirements are made available by the present invention.